Manufacture of metal articles or masses



Patented Sept. 3, i940 TEN.

William David Jones and Edward James Groom,

London, England h v No Drawing. Application February 11, 1938, Se-

rial No. 190,138. In Great Britain October 18,

4 (Jlaims.

This invention relates to the manufacture of metal articles or masses.

An object of this invention is to provide sintered metal articles ormasses from initial ma- 5 terials which have not previously beenemployed for sintering.

A further object of this invention is to provide metal articles bysintering which either cannot be made by casting or which it is notpracticable or economic to make by casting.

A still further object of this invention is to provide a process forproducing the aforesaid sintered metal articles or masses.

According to the invention a process is provided for the manufacture ofmetal articles or masses wherein a powder which is an alloy of iron andcarbon with or without small proportions of other constituents whichalloy isnormally brittle in the cold cast condition is sintered orpartially sintered by heating to a temperature below that of general orcomplete fusion of the alloy, preferably with the application ofpressure before, during or after the heating, to cause agglomeration ofthe particles of powder with formation of the article or mass, theheating being effected in the presence of the small pro-. portion ofimpurity which is commonly present in the alloy and/or with a smallproportion of impurity mixed therewith and which has a bond- 80 mgaction on the particles during the heating.

The process by which it is possible to cause the particles of an alloyof iron and carbon which is normally brittle in the cold cast condition,for example a white cast iron powder prepared by grinding, blowing, orpreferably by granulating to agglomerate together under the influence ofpressure and heat with the production of articles of high tensilestrength and hardness appears to be connected with the action of thevarious impurities in the alloy particularly with the phosphorus contentwhen phosphorus constitutes an important impurity. It appears that attemperatures higher than 950 C. a fusible constituent consistingof analloy of iron rich in phosphorus t5 and carbon is formed in ironmixtures which contain sufflcient of these elements to permit of itsformation.

This fusible constituent appears to be important in that it acts as acement or binder for the particles of the alloy and when present, itgenerally leads to the production of superior physical properties. It isobvious that as a starting material it is possible to use:

(i) An alloy of iron and any desired quantity of carbon that containsthe correct percentage of impurities (for example phosphorus) for the Isuccessful formation of a fusible constituent.

x (it) An alloy that is deficient in such impurities such as steelturnings, or cast iron drillings or borings, which are low in phosphoruscontent. 5 In this case it is always possible to make good thisdeficiency by adding to the alloy small amounts of impurities. Forexample, in the case of cast iron borings which are lowin phosphoruscontent it is possible to add to such borings small amounts of redphosphorus, or small amounts of an alloy rich in phosphorus such asferro-phosphorus, phosphor-copper, phosphor-nickel or phosphor-tin. Itis also possible to make good the deficiency of such materials inimpurities by adding to them other impurities than those which arenormally found in them.

(iii) An alloy that is too rich in certain impurities. It is possiblefor example to have an alloy of iron. that contains so much carbon orsulphur that the physical properties of the finished article would beseriously prejudiced, or to have an alloy containing so much phosphorusthat. an undue amount of bonding or cementing agent was formed at thetemperature employed and which might cause difficulties in connectionwith wear of the mould or with extraction of the article from the mould.In such cases as these it is always possible to dilute such impuritiesand to reduce their influence by adding to the iron alloy to be sinteredan alloy of iron which is particularly low in such impurities such as apure iron powder or a decarburized cast iron grit or shot.

It will be understood that if the powder is subjected to pressure beforethe heating it may also be subjected to pressure during and/or after theheating and likewise if the powder is subjected to pressure during theheating it may also be subjected to pressure after heating.

The heating may be effected in any desired manner for example heating bygas or electricity. When the heating is effected electrically the powdermay be used as a heating resistance.

The process may be carried out with the aid of dies, moulds, or pressesand in general a temperature between about 700 and 1200 C. will beemployed. Suitable pressures are between about I 2 and 60 tons/sq. in.

- It is preferred to use as the initial material a cast iron powderfiner than 60 mesh (I. M. M. sieve) and from the point of view ofcheapness it is advantageous to use a cast iron powder which is atpresent a by-product, for example a cast iron grit or shot finer than 60mesh and all g I smegma kinds of cast iron borings, millings anddrillings which can easily be crushed to powders finer than 60 mesh.Fines produced as waste in the manufacture of ferro-silicon,term-vanadium, 5 ferro-titanium and the like may be added to the castiron if desired. Cast irons or pig irons prepared in the blast furnacein the usual manner or prepared by low temperature reduction processesin the form of spongeor powder containing w more than 0.5% of phosphorusand cast irons containing more than 0.5% of silicon are particularlyadvantageous as initial materials for the process of the presentinvention.

Moreover it is known that the mechanical propl5 erties of theiron-carbon alloys are influenced to a considerable extent by thecontent and distribution of iron oxide. It is also a fact that it isdifficult or impossible to control with any degree of accuracy both theamount and distribugo tion of this oxide by ordinary techniques ofcasting mainly owing to the considerable difference in specific gravitybetween iron and its oxide and the mechanical diificulties involved indistributing by stirring a mass of fine iron oxide powder 25 into a meltof molten iron alloy at high temperatures. The process of the presentinvention however has the additional advantage that it renders hotpressing, or by admixture with the powder 40 of oxidising agents such asmanganese dioxide. The fragility of masses made in this way can becontrolled within very fine limits, and the mode in which fracture takesplace under stress is also capable of control. This is of particularadvantage in the case of vessels, containers or receptacles intended tocontain explosives and designed to be disrupted by the explosive chargecontained within them. Examples of the above are as follows: shots forshot firing purposes intended to be loaded with solid carbon dioxide andemployed for disrupting masses of stone, or bombs for use in warfare.-

The following examples illustrate how the process of the invention maybe carried into ef- 1. A white cast iron powder the particles of whichhave an average diameter of less than ,6 of an inch is introduced into acircular die '0 which is maintained at a temperature of 1000" C. Thepowder is then pressed at 10 tons/sq. in. by means of a quick actingpress and a compact is produced having a tensile strength of 31 tons/sq.in. and a Brinell number of 254. This compact a after suitable machiningis used as an orifice disc,

2. A cast iron gear wheel was produced by pressing the powder referredto in Example 1 in a die which is the female counterpart of the gearwheel at a pressure of 5 tons per sq. in. at 1050' C.

n The pressing had a Brinell number of 269 and was found to have apearlitic structure when examined under the microscope. The article washeated at 800 C. for 20 minutes in a gas fired mume furnace and thenquenched in sperm 011.

After this treatment the Brinell number was 415 and on examination underthe microscope the article was found to have a sorbitic structure.

According to the physical properties desired in the finished articlethepowder particles during treatment may be surrounded by an oxidising, 5neutral or reducing atmosphere. Normally, it is preferred to employ airas the atmosphere but in certain calses according to the processescustomary in the manufacture of articles from metal powders,.it ispreferred to blow a stream-of hy- .10 drogen or other reducing gas intothe mould or die or to mix with the alloy powder a solid substance suchas charcoal which on being heated will produce a reducing atmosphere.

The process of the present invention enables articles to be produced insuch shapes and/or sizes which hitherto could only be produced inbrittle or hard alloys of iron and carbon by the processes of casting,die casting or by the machining of castings. Examples of such materialsI which are brittle and impossible or dimcult or uneconomic tomanufacture to specific shapesother than by the processes of casting ormachining are high carbon steels of the type usually known as toolsteels, and cast irons-more particularly those having their carboncontent chiefly in the form of iron carbide (FeaC) cast irons containingmore than .5% of phosphorus and cast irons-containing more than 0.5% ofsilicon.

By the process of the present invention it is 80 possible to manufacturewith brittle iron-carbon alloys such articles as gear wheels or blanks,spurwheels, crankshafts, cam shafts, pistons, cylinder liners, pinions,racks, and the like which previous-- 1y have had to be made by castingor the machin- .86 ing of castings and where forging, such as isemployed in the shaping of less brittle alloys of lower carbon contentis an impossible operation.

Further examples of articles or masses which can be made by the processof the invention are all components with thin sections, or abruptchanges in section, which, produced by ordinary casting methods, are aptto possess non-uniform microstructures and physical properties. Blocks,

bars, billets and sections for subsequent machin- 4!! ing purposes, andit should be noted that these materials can bemanufactured in acondition having remarkable free cutting properties. Washers, rings,thrust rings and spacers which are usually characterised by thinsections but required to possess high strength. Containers or vesselsrequired to possess the property of being permeable to gases or liquids,or to be easily ruptured by the discharge of explosives contained withinthem, but possessing at the same time mechanical properties which renderthem workable by ordinary machining processes, and capable of beinghandled in the ordinary manner without fear of breakage. Componentsrequiring extremely dense structures impermeable 60 to gases or liquidsand of high strength andv resistance to abrasion or corrosion such ascocks, spigots, plugs, cover-plates, valves, unions in chemical plant,hydraulic or oil equipment. The production of a material possessingspecial structures unobtainable by normal casting or forgingtechniquensuch as a controlled zoned structure, or a structurecharacterised by the distribution of one or more of themicro-constituents in a predetermined manner. The production ofstructures 7 characterised by the presence of microstructures of apre-determined size, shape or distribution. The production of articlescharacterised by the predetermined occurrence oflocalised areas orvolumes possessing special physical, chemical or 16 mechanicalproperties, but forming at the same time integral parts of the whole, e.g. areas of a 10% silicon heat and corrosion resisting iron may beproduced in a matrix of a low silicon iron. The production of articlescharacterised by the fact that they are formed around and have embeddedin them some pre-formed component, e. g. metallic or non-metallic tubes,insulated heating elements, .or inclusions of a higher or lower densitythan the main body of the article in order to obtain specialisedmechanical or balance characteristics, e. g. tungsten spheres may beembedded in the nose of bullets or other projectiles made by theprocesses described. The production of articles for simultaneous orsubsequent forging, pressing, stamping, extrusion, or impact extrusion.The utilisation for high duty structural components of high phosphorusand/or high sulphur iron alloys normally considered as too brittle forsuch uses without preliminary metallurgical treatment to remove excessphosphorus and/or sulphur. Some particular instances of the above are:

In connection with steam, gas, hydraulic, or

internal combustion engines, cylinders, heads,

bushings, stuffing box glands, neck rings, piston rings, connectingrods, valves, valve seats, shoes,

rods, bearings, and bearing caps, governor parts and rocker arms.

In connection with tubular goods and hydraulic and oil equipment,couplings, flanges, pipe unions, spools, casings, shoes, guides,bafile-plates, oriflce discs, pipe T's, standard and high pressure bullplugs and caps, flowbeams, cocks, oil jets, flow plugs, nozzles andinjectors.

Miscellaneous-prepressings to be reshaped and repressed, welding rods,pulleys, sprockets, nuts, bolts, screws, shackles, keys, pins, hooks,hinges, handles, clips, knobs, fasteners, chains, brackets, contacts,plates, moulds for pressing operations, bearing housings, for encasingand connecting objects, cone seatings and rivets and cones for clutches.

Improved physical properties can also be obtained in the finishedpressing by means of a suitable heat-treatment. In the case of powdersobtained from grey cast irons, in some cases the presence offreegraphite may interfere with ence of brittle envelopes surroundingthe individual grains of the alloy such as are frequently inherent in acasting process with certain alloys are, owing to the absence of generalfusion in the process of the present invention, entirely avoided. Thusit is possible by a choice of opstamping,

herent in casting, melting and slagging processes,

the use of permanent or semi-permanent moulds, accuracy of sizing, andavoidance of wastage of material in the form of risers and headers.

It will be appreciated that the present invention is not limited to theuse of the ironcarbon alloys, hereinbefore specifically referred to butincludes the use of all those alloys containing iron and carbon as theirchief alloying constituents and which are normally brittle in the coldcast condition.

Examples of other constituents which may be present are nickel,chromium, titanium, molybdenum, vanadium, silicon, phosphorus, sulphur,aluminium oxide, silica, titanium dioxide and other metals or refractory'oxides. Refractory oxides such as magnesium oxide or aluminium oxideare valuable additions when it is desired to control the fragility ofthe iron-carbon alloy.

The masses and articles produced according to the present inventionpreferably have physical properties within the following ranges:

Tensile strength'4 to 35 tons per sq. in., per cent elongation Q to 1}Brinell No. 120 to 300 in the annealed condition and 200 to 550 in theheat treated condition, Izod impact value 0 to Sit. lbs.

By the expression "alloy which is normally brittle in the cold castcondition" as used herein is meant one which, when fractured underapplied stress does so with less than a 1% increase in its lineardimensions.

The term sinterin-g as used herein includes fritting that is anoperation in which partial fusion of the alloy or the impurities takesplace.

The term article as used in the appended claims includes mass.

What we claim is:

1. As a new article of manufacture, a sintered agglomerated powder ofwhite cast iron bonded by an iron-carbon-phosphorus eutectic.

2. A process for the manufacture of a metal article, comprising heatinga powder of white cast iron containing more than 0.5% of phosphorus asan impurity to a temperature below that of general or complete fusion ofthe alloy but sufllcient to produce at least partial sintering of thepowder.

3. As a new article of manufacture, a sintered agglomerated powder of analloy of iron' and carbon bonded by an iron-phosphorus eutectic.

4. As a new article of manufacture, a sintered agglomerated powderofwhite cast iron bonded by. an iron-phosphorus eutectic.

WILLIAM DAVID JONES. EDWARD, JAMES hRoqM.

